1. Field of the Invention
This invention relates to fiber-forming, melt-spinnable wholly aromatic copolyesters prepared from hydroquinone, chloro- or methylhydroquinone, terephthalic acid and a carboxy-hydroxybenzophenone. The invention includes filaments of the polyester prepared from optically anisotropic melts and having high modulus in the as-spun condition and high tenacity after heat treatment.
2. Description of the Prior Art
Aromatic copolyesters capable of forming anisotropic melts and containing units derived from hydroquinone, chlorohydroquinone or methylhydroquinone and terephthalic acid have been disclosed in prior art patents U.S. Pat. Nos. 4,118,372; 4,075,262; 3,991,014, 4,066,620; 3,991,013; 4,146,702, 4,156,070 and 4,256,624. In each case a third component is incorporated to reduce the melt flow temperature so that melt spinning can be accomplished without polymer degradation.
Polyesters made entirely from carboxy-hydroxy-benzophenones are disclosed in U.S. Pat. No. 3,531,435. There is no disclosure of copolymers wherein the benzophenone derivative is a minor constituent (i.e., less than 50 mole %).
More recently in U.S. Pat. No. 4,232,144 units derived from 3-carboxy-4-hydroxy-benzophenone are disclosed in combination with units derived from 4-hydroxy-benzoic acid, hydroquinone and terephthalic acid to provide melt-spinnable polyesters. In U.S. Pat. No. 4,232,144 the units derived from 4-hydroxy-benzoic acid are present in major amounts.